JP7119940B2 - Negative electrode active material composite for all-solid-state battery - Google Patents
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Description
本開示は全固体電池用負極活物質複合体に関する。 TECHNICAL FIELD The present disclosure relates to a negative electrode active material composite for an all-solid-state battery.
リチウムイオン電池等の電池の分野において、電解液の代わりに固体電解質を使用する全固体電池の開発が行われている。全固体電池は、電池内に可燃性の有機溶媒を用いないので、安全装置の簡素化が図れ、製造コストや生産性に優れると考えられている。
また、リチウムイオン電池の負極活物質として、従来広く使用されている炭素系負極活物質よりも、容量の大きい負極活物質として、ケイ素、錫等の合金系負極活物質の使用が試みられている。
しかし、合金系負極活物質を用いた全固体電池は、充放電に伴い、合金系負極活物質が膨張収縮することにより、合金系負極活物質と他の材料との間に空隙が生じ、空隙によって電子伝導パスとイオン伝導パスが切断され、抵抗が増加したり、容量が低下する等、サイクル特性が低下しやすいという問題がある。
In the field of batteries such as lithium-ion batteries, development of all-solid-state batteries using a solid electrolyte instead of an electrolytic solution is underway. An all-solid-state battery does not use a combustible organic solvent in the battery, so it is thought that the safety device can be simplified and the manufacturing cost and productivity are excellent.
In addition, as a negative electrode active material for lithium ion batteries, the use of alloy-based negative electrode active materials such as silicon and tin has been attempted as a negative electrode active material having a larger capacity than the carbon-based negative electrode active materials that have been widely used in the past. .
However, in an all-solid-state battery using an alloy-based negative electrode active material, the alloy-based negative electrode active material expands and shrinks during charging and discharging, resulting in the formation of voids between the alloy-based negative electrode active material and other materials. There is a problem that the electronic conduction path and the ion conduction path are cut off by , and the cycle characteristics tend to deteriorate, such as an increase in resistance and a decrease in capacity.
本出願人は、特許文献１に、合金系負極活物質を用いた全固体電池のサイクル特性を向上する電池システムとして、アモルファス化率を特定の範囲にした合金系負極活物質粒子と、特定の条件を満たすように充放電電圧を制御する制御装置とを用いた電池システムを開示している。
一方、電解液を用いたリチウムイオン電池では、負極活物質として炭素系材料とケイ素系材料との複合材料を用いることが提案されている（例えば特許文献２～４）。
The present applicant discloses in Patent Document 1 that, as a battery system for improving the cycle characteristics of an all-solid-state battery using an alloy-based negative electrode active material, alloy-based negative electrode active material particles having an amorphization rate in a specific range and a specific A battery system using a controller that controls charging and discharging voltages to satisfy conditions is disclosed.
On the other hand, in a lithium ion battery using an electrolytic solution, it has been proposed to use a composite material of a carbon-based material and a silicon-based material as a negative electrode active material (for example,
しかしながら、合金系負極活物質を用いた電池は、充電後に所定期間保存した場合、放電容量が低下するという問題があり、保存特性の向上が求められている。
上記実情を鑑み、本開示では、電池を充電後に所定期間保存した際の容量の低下を抑制可能な全固体電池用負極活物質複合体を提供することを目的とする。
However, a battery using an alloy-based negative electrode active material has a problem of a decrease in discharge capacity when stored for a predetermined period after charging, and improvement in storage characteristics is desired.
In view of the above circumstances, an object of the present disclosure is to provide a negative electrode active material composite for an all-solid-state battery that can suppress a decrease in capacity when the battery is stored for a predetermined period after charging.
本開示の全固体電池用負極活物質複合体は、炭素繊維と、前記炭素繊維の表面を被覆するＳｉ層とを有し、
前記炭素繊維の長手方向に垂直な方向に切断した断面内での前記Ｓｉ層の膜厚の変動係数が０．４以下であることを特徴とする。
The negative electrode active material composite for an all-solid-state battery of the present disclosure has carbon fibers and a Si layer covering the surface of the carbon fibers,
A variation coefficient of the film thickness of the Si layer in a cross section cut in a direction perpendicular to the longitudinal direction of the carbon fiber is 0.4 or less.
本開示によれば、断面内でのＳｉ層の膜厚の変動係数が０．４以下であり、Ｓｉ層の膜厚の均一性に優れることから、電池を充電後に所定期間保存した際の放電容量の低下を抑制可能な全固体電池用負極活物質複合体を提供することができる。 According to the present disclosure, the coefficient of variation of the thickness of the Si layer in the cross section is 0.4 or less, and the uniformity of the thickness of the Si layer is excellent. It is possible to provide a negative electrode active material composite for an all-solid-state battery capable of suppressing a decrease in capacity.
本開示の全固体電池用負極活物質複合体は、炭素繊維と、前記炭素繊維の表面を被覆するＳｉ層とを有し、
前記炭素繊維の長手方向に垂直な方向に切断した断面内での前記Ｓｉ層の膜厚の変動係数が０．４以下であることを特徴とする。
The negative electrode active material composite for an all-solid-state battery of the present disclosure has carbon fibers and a Si layer covering the surface of the carbon fibers,
A variation coefficient of the film thickness of the Si layer in a cross section cut in a direction perpendicular to the longitudinal direction of the carbon fiber is 0.4 or less.
本発明者は、炭素繊維の表面にＳｉ層を設けた負極活物質複合体を非水電解液電池に用いると、後述する比較例２と比較例３との対比から示されるように、Ｓｉ単体を負極活物質として用いた場合に比べ、充電後に所定期間保存した際の放電容量が低下しやすく、保存特性が低下することを見出した。また、本発明者は、特許文献２～４に開示された手法で、炭素繊維の表面にＳｉ層を形成した複合体を全固体電池に用いた場合も、保存特性が低下しやすいことを知見した。
それに対し、本開示の全固体電池用負極活物質複合体を用いた全固体電池は、Ｓｉ単体を負極活物質として用いた全固体電池に比べ、保存特性が向上するという、非水電解液電池とは反対の意外な効果を有する。
非水電解液電池では、Ｓｉ系の負極活物質を用いると、電解液の分解反応が起きやすく、分解物が発生して抵抗の高い被膜となることや、リチウムの失活が起きることにより、容量が低下しやすいと考えられる。炭素繊維の表面にＳｉ層を設けた負極活物質複合体は、Ｓｉ粉末等の従来のＳｉ系の負極活物質よりもＳｉの表面積が大きいため、電解液を用いたリチウムイオン電池に用いると、電解液の分解反応がより起きやすくなって、保存特性が更に低下すると推定される。
一方、全固体電池では、電解液の代わりに固体電解質層を用いるため、電解質の分解反応による容量の低下が小さい。しかし、全固体電池においても、Ｓｉ単体や、特許文献２～４に開示された手法で炭素繊維の表面にＳｉ層を形成した複合体を、負極活物質として用いた場合は、保存特性が低下する場合がある。
Ｓｉ単体を負極活物質として用いた場合は、Ｓｉと固体電解質との接触界面を維持し難いため、保存特性が低下しやすいと推定される。
特許文献２～４の手法では、炭素繊維全体に、Ｓｉ層を均一な膜厚で形成することが困難なため、炭素繊維がＳｉ層に被覆されずに露出した部分があったり、粒径の大きいＳｉの粒子が形成されたり、Ｓｉ層が局所的、つまり表面だけに厚くなって、Ｓｉ層同士が互いに付着したりすることで、副反応が生じやすく、また、電極内の反応が不均一になりやすいため、保存特性が低下しやすいと推定される。炭素材料と接している固体電解質の表面には酸素の局在化が観察されるため、負極活物質複合体の表面に炭素繊維が露出していると、固体電解質と接触したときに何らかの分解反応が起きて、リチウムが消費されると推定される。また、Ｓｉ層同士が互いに付着すると、電極内の反応が不均一になって、電子伝導パス及びイオン伝導パスの切断や、化学的な副反応が起きやすいと推定される。
それに対し、本開示の全固体電池用負極活物質複合体は、長手方向に垂直な方向に切断した断面内でのＳｉ層の膜厚の変動係数が０．４以下であることから、Ｓｉ層の均一性に優れ、炭素繊維が露出した部分が無い又はほとんど無いため、μｍオーダーの電子伝導パスとイオン伝導パスを両立することができると推定される。μｍオーダーの電子伝導パスとイオン伝導パスがあれば、Ｓｉ活物質の膨張収縮によってＳｉと固体電解質の接触界面の一部が離れたとしても、他の接触界面からの電子伝導とイオン伝導によって充放電に寄与できる割合が高くなると考えられる。また、本開示の全固体電池用負極活物質複合体は、Ｓｉ層の膜厚の均一性に優れることにより、負極活物質複合体間でＳｉ層同士が付着し難いため、電極内の反応が均一になりやすく、局部的な膨張や副反応が抑制される結果、放電容量が維持されやすく、保存特性の低下を抑制することができると推定される。なお、本開示において、保存特性が低下するとは、電池を充電後、所定期間保存した場合における保存前後での容量維持率が低下することをいう。
更に、本開示の全固体電池用負極活物質複合体は、炭素繊維を有するため、負極活物質としてＳｉ単体を用いる場合よりも、負極の抵抗を低減することができる。本開示の全固体電池用負極活物質複合体を用いた負極は、抵抗を低く維持しやすいため、負極中の負極活物質の含有割合を多くすることができる。
The present inventors have found that when a negative electrode active material composite in which a Si layer is provided on the surface of carbon fibers is used in a non-aqueous electrolyte battery, as shown by comparison between Comparative Examples 2 and 3 described later, Si alone is used as the negative electrode active material, the discharge capacity tends to decrease when stored for a predetermined period after charging, and storage characteristics deteriorate. In addition, the inventors of the present invention have found that storage characteristics tend to deteriorate even when a composite in which a Si layer is formed on the surface of carbon fibers is used in an all-solid-state battery by the methods disclosed in
On the other hand, an all-solid-state battery using the negative electrode active material composite for an all-solid-state battery of the present disclosure has improved storage characteristics compared to an all-solid-state battery using Si alone as a negative electrode active material. has the surprising opposite effect.
In non-aqueous electrolyte batteries, when a Si-based negative electrode active material is used, the decomposition reaction of the electrolyte is likely to occur, and decomposition products are generated to form a film with high resistance, and deactivation of lithium occurs. It is thought that the capacity tends to decrease. A negative electrode active material composite in which a Si layer is provided on the surface of carbon fibers has a larger surface area of Si than a conventional Si-based negative electrode active material such as Si powder. It is presumed that the decomposition reaction of the electrolytic solution is more likely to occur, and the storage characteristics are further deteriorated.
On the other hand, in all-solid-state batteries, a solid electrolyte layer is used instead of an electrolytic solution, so that the decrease in capacity caused by the decomposition reaction of the electrolyte is small. However, even in all-solid-state batteries, when Si alone or a composite in which a Si layer is formed on the surface of carbon fibers by the method disclosed in
It is presumed that when simple Si is used as the negative electrode active material, it is difficult to maintain the contact interface between Si and the solid electrolyte, and the storage characteristics tend to deteriorate.
In the methods of
On the other hand, in the negative electrode active material composite for an all-solid-state battery of the present disclosure, the coefficient of variation of the thickness of the Si layer in the cross section cut in the direction perpendicular to the longitudinal direction is 0.4 or less. , and there is no or almost no exposed portion of the carbon fiber. If there is an electronic conduction path and an ionic conduction path on the order of μm, even if a part of the contact interface between the Si and the solid electrolyte separates due to the expansion and contraction of the Si active material, the electronic conduction and ionic conduction from the other contact interface will cause charging. It is considered that the proportion that can contribute to discharge increases. In addition, since the negative electrode active material composite for an all-solid-state battery of the present disclosure is excellent in the uniformity of the film thickness of the Si layer, the Si layers hardly adhere to each other between the negative electrode active material composites, so the reaction in the electrode It is presumed that as a result of easy uniformity and suppression of local swelling and side reactions, the discharge capacity can be easily maintained and deterioration of storage characteristics can be suppressed. In the present disclosure, deterioration in storage characteristics means deterioration in capacity retention rate before and after storage when the battery is stored for a predetermined period of time after being charged.
Furthermore, since the negative electrode active material composite for an all-solid-state battery of the present disclosure has carbon fibers, it is possible to reduce the resistance of the negative electrode as compared with the case of using simple Si as the negative electrode active material. Since the negative electrode using the negative electrode active material composite for an all-solid-state battery of the present disclosure tends to maintain low resistance, the content of the negative electrode active material in the negative electrode can be increased.
図１は、本開示の全固体電池用負極活物質複合体の一例を示す断面模式図である。図１に示す全固体電池用負極活物質複合体１０は、炭素繊維１と、前記炭素繊維１の表面を被覆するＳｉ層２とを有する。
FIG. 1 is a cross-sectional schematic diagram showing an example of a negative electrode active material composite for an all-solid-state battery of the present disclosure. A negative electrode
１．炭素繊維
本開示の全固体電池用負極活物質複合体が有する炭素繊維は、繊維状の炭素材料であれば、特に限定はされず、例えば、気相成長炭素繊維（ＶＧＣＦ）、カーボンナノチューブ、ＰＡＮ系の炭素繊維、ピッチ系の炭素繊維、レーヨン系の炭素繊維、セルロース等の天然の炭素系の繊維を分離して熱処理工程を経て作られる炭素繊維、多孔質炭素繊維等の公知の炭素繊維を用いることができる。中でも、炭素繊維の表面にＳｉ層が均一に形成されやすく、全固体電池の保存特性を向上し易い点から、気相成長炭素繊維（ＶＧＣＦ）が好ましい。
1. Carbon fiber The carbon fiber included in the negative electrode active material composite for an all-solid-state battery of the present disclosure is not particularly limited as long as it is a fibrous carbon material. For example, vapor grown carbon fiber (VGCF), carbon nanotube, PAN well-known carbon fibers such as carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, carbon fibers made by separating natural carbon-based fibers such as cellulose and undergoing a heat treatment process, and porous carbon fibers. can be used. Among them, vapor grown carbon fiber (VGCF) is preferable because a Si layer is easily formed uniformly on the surface of the carbon fiber and the storage characteristics of the all-solid-state battery are easily improved.
前記炭素繊維の繊維径及び繊維長は、特に限定はされないが、炭素繊維の表面にＳｉ層が均一に形成されやすく、全固体電池の保存特性を向上し易い点から、繊維径は０．１μｍ以上０．３μｍ以下の範囲内であることが好ましく、繊維長は１μｍ以上であることが好ましい。なお、本開示において繊維径とは、繊維を長手方向に対し垂直な方向に切断したときの当該繊維の断面の最大径をいう。 The fiber diameter and fiber length of the carbon fiber are not particularly limited, but the fiber diameter is 0.1 μm because the Si layer is easily formed uniformly on the surface of the carbon fiber and the storage characteristics of the all-solid-state battery are easily improved. The fiber length is preferably in the range of 0.3 μm or less, and the fiber length is preferably 1 μm or more. In the present disclosure, the fiber diameter refers to the maximum diameter of the cross section of the fiber when the fiber is cut in the direction perpendicular to the longitudinal direction.
また、特に限定はされないが、炭素繊維の表面にＳｉ層が均一に形成されやすく、全固体電池の保存特性を向上し易い点から、前記炭素繊維の比表面積は、１０ｍ２／ｇ以上３０ｍ２／ｇ以下であることが好ましい。 In addition, although not particularly limited, the specific surface area of the carbon fiber is preferably 10 m 2 /g or more and 30 m 2 because the Si layer is easily formed uniformly on the surface of the carbon fiber and the storage characteristics of the all-solid-state battery are easily improved. /g or less.
２．Ｓｉ層
本開示の全固体電池用負極活物質複合体は、前記炭素繊維の表面を被覆するＳｉ層を有する。前記Ｓｉ層は、前記炭素繊維の表面に形成されたケイ素（Ｓｉ）を主成分とする被膜であり、効果を損なわない範囲において、ケイ素と合金を形成する金属及びドープ元素等を含有していてもよい。前記Ｓｉ層中のケイ素（Ｓｉ）の含有量は、特に限定はされないが、高容量化の観点から、前記Ｓｉ層の総量を１００質量％とした場合に、９０質量％以上であることが好ましい。
前記Ｓｉ層が含有していてもよいケイ素と合金を形成する金属としては、例えば、Ｌｉ、Ｎａ、Ｍｇ、Ａｌ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｔｉ、Ｚｒ、Ｈｆ等が挙げられる。前記Ｓｉ層が含有していてもよいドープ元素としては、例えば、Ｂ、Ｐ、Ｇａ、Ａｓ、Ｓｂ等が挙げられる。
2. Si Layer The negative electrode active material composite for an all-solid-state battery of the present disclosure has a Si layer covering the surface of the carbon fiber. The Si layer is a coating mainly composed of silicon (Si) formed on the surface of the carbon fiber, and contains a metal forming an alloy with silicon, a dope element, etc. within a range that does not impair the effect. good too. The content of silicon (Si) in the Si layer is not particularly limited, but from the viewpoint of increasing the capacity, it is preferably 90% by mass or more when the total amount of the Si layer is 100% by mass. .
Examples of the metal that forms an alloy with silicon that may be contained in the Si layer include Li, Na, Mg, Al, Cr, Mn, Fe, Co, Ni, Cu, Ti, Zr, and Hf. be done. Examples of doping elements that the Si layer may contain include B, P, Ga, As, and Sb.
本開示の全固体電池用負極活物質複合体は、前記炭素繊維の長手方向に垂直な方向に切断した断面内での前記Ｓｉ層の膜厚の変動係数が０．４以下である。これにより、本開示の全固体電池用負極活物質複合体を負極活物質として用いた全固体電池は、充電後に所定期間保存した際の容量の低下が抑制される。
前記Ｓｉ層の膜厚の変動係数は、本開示の全固体電池用負極活物質複合体を、長手方向に垂直な方向に切断して得られる断面内で、前記Ｓｉ層の膜厚を８方向で測定したときの測定値の標準偏差を、測定値の平均値で除してなる値（変動係数＝標準偏差／平均値）である。ここで、前記Ｓｉ層の測定箇所を図１を参照して説明する。全固体電池用負極活物質複合体１０の断面において、炭素繊維１の断面の重心を中心点Ｃとし、当該中心点Ｃを通る任意の直線を基準線Ｌ０と定め、当該基準線Ｌ０と、前記中心点Ｃを通り且つ前記基準線Ｌ０とのなす角が９０°である直線Ｌ１と、前記中心点Ｃを通り且つ前記基準線Ｌ０とのなす角が４５°である直線Ｌ２及び直線Ｌ３とを引いたときに、これらの直線Ｌ０、Ｌ１、Ｌ２及びＬ３が通るＳｉ層上の計８ヶ所ｔ１～ｔ８におけるＳｉ層の厚みを、前記変動係数を求める際に用いる８方向でのＳｉ層の膜厚とする。
全固体電池の保存特性を向上する観点から、前記Ｓｉ層の膜厚の前記変動係数は、０．３９以下であることが好ましい。
前記Ｓｉ層の膜厚の前記変動係数の下限は、特に限定はされず、例えば０．０５以上であってもよく、０．１０以上であってもよい。
なお、Ｓｉ層の膜厚を測定する際に用いる全固体電池用負極活物質複合体の断面は、例えば、全固体電池用負極活物質複合体をエポキン樹脂等で樹脂包埋したサンプルを、イオンミリングすることにより得ることができる。前記断面の観察は、例えば、走査型電子顕微鏡（ＳＥＭ）を用いて行うことができる。
In the negative electrode active material composite for an all-solid-state battery of the present disclosure, the Si layer has a thickness variation coefficient of 0.4 or less in a cross section taken in a direction perpendicular to the longitudinal direction of the carbon fibers. As a result, an all-solid-state battery using the negative electrode active material composite for an all-solid-state battery of the present disclosure as a negative electrode active material is prevented from decreasing in capacity when stored for a predetermined period after charging.
The coefficient of variation of the thickness of the Si layer is the thickness of the Si layer in the cross section obtained by cutting the negative electrode active material composite for an all-solid-state battery of the present disclosure in a direction perpendicular to the longitudinal direction. It is a value (variation coefficient = standard deviation / average value) obtained by dividing the standard deviation of the measured values by the average value of the measured values. Here, the measurement points of the Si layer will be described with reference to FIG. In the cross section of the negative electrode
From the viewpoint of improving the storage characteristics of the all-solid-state battery, the variation coefficient of the film thickness of the Si layer is preferably 0.39 or less.
The lower limit of the coefficient of variation of the film thickness of the Si layer is not particularly limited, and may be, for example, 0.05 or more, or 0.10 or more.
The cross section of the negative electrode active material composite for all-solid-state batteries used when measuring the film thickness of the Si layer is obtained by, for example, embedding a sample of the negative-electrode active material composite for all-solid-state batteries in epoxy resin or the like. It can be obtained by milling. Observation of the cross section can be performed using, for example, a scanning electron microscope (SEM).
前記Ｓｉ層の膜厚は、２０ｎｍ以上４００ｎｍ以下の範囲内であることが好ましく、２５ｎｍ以上３７０ｎｍ以下の範囲内であることがより好ましく、２９ｎｍ以上３６８ｎｍ以下の範囲内であることがより更に好ましい。
また、本開示の全固体電池用負極活物質複合体を長手方向に垂直な方向に切断して得られる１つの断面内での前記Ｓｉ層の膜厚の平均値は、３０ｎｍ以上３００ｎｍ以下であることが好ましく、３５ｎｍ以上２５０ｎｍ以下であることがより好ましく、３９ｎｍ以上２０８ｎｍ以下であることがより更に好ましい。
The thickness of the Si layer is preferably 20 nm or more and 400 nm or less, more preferably 25 nm or more and 370 nm or less, and even more preferably 29 nm or more and 368 nm or less.
Further, the average value of the film thickness of the Si layer in one cross section obtained by cutting the negative electrode active material composite for an all-solid-state battery of the present disclosure in a direction perpendicular to the longitudinal direction is 30 nm or more and 300 nm or less. , more preferably 35 nm or more and 250 nm or less, and even more preferably 39 nm or more and 208 nm or less.
また、本開示の全固体電池用負極活物質複合体の全体における前記Ｓｉ層の膜厚の変動係数は、０．４超過であってもよく、特に限定はされないが、全固体電池の保存特性を向上しやすい点から、０．６５以下であることが好ましい。 In addition, the variation coefficient of the thickness of the Si layer in the entire negative electrode active material composite for an all-solid-state battery of the present disclosure may exceed 0.4, and is not particularly limited, but the storage characteristics of the all-solid-state battery is preferably 0.65 or less because it is easy to improve the
本開示の全固体電池用負極活物質複合体が含有するＳｉの含有量は、特に限定はされないが、高容量化の観点から、負極活物質複合体の総量１００質量％に対し、４５質量％以上であることが好ましく、全固体電池の保存特性を向上する点及び抵抗を低減する点から、９８質量％以下であることが好ましく、９７質量％以下であることがより好ましく、７０質量％以下であることがより更に好ましい。 The content of Si contained in the negative electrode active material composite for an all-solid-state battery of the present disclosure is not particularly limited, but from the viewpoint of increasing the capacity, it is 45% by mass with respect to 100% by mass of the total amount of the negative electrode active material composite. It is preferably 98% by mass or less, more preferably 97% by mass or less, and 70% by mass or less from the viewpoint of improving the storage characteristics of the all-solid-state battery and reducing the resistance. is even more preferable.
本開示の全固体電池用負極活物質複合体の表面積１００％中、前記Ｓｉ層で被覆された面積は、特に限定はされないが、全固体電池の保存特性を向上する点から、９０％以上であることが好ましく、９５％以上であることがより好ましく、９８％以上であることがより更に好ましく、炭素繊維の表面全体がＳｉ層で被覆されてなることが最も好ましい。 In the surface area of 100% of the negative electrode active material composite for an all-solid-state battery of the present disclosure, the area covered with the Si layer is not particularly limited, but from the viewpoint of improving the storage characteristics of the all-solid-state battery, it is 90% or more. It is preferably 95% or more, even more preferably 98% or more, and most preferably the entire surface of the carbon fiber is covered with the Si layer.
３．Ｓｉ層の形成方法
前記Ｓｉ層の形成方法は、前記炭素繊維の長手方向に垂直な方向に切断した断面内でのＳｉ層の膜厚の変動係数が０．４以下となるように、前記炭素繊維の表面にＳｉ層を形成できる方法であればよく、特に限定はされないが、Ｓｉ層の膜厚が均一になりやすい点から、バレルスパッタリング法が好ましい。
3. Method of forming Si layer In the method of forming the Si layer, the carbon fibers are formed such that the coefficient of variation of the film thickness of the Si layer in a cross section taken in a direction perpendicular to the longitudinal direction of the carbon fibers is 0.4 or less. The method is not particularly limited as long as it can form a Si layer on the surface of the fiber, but the barrel sputtering method is preferred because the film thickness of the Si layer is likely to be uniform.
バレルスパッタリング法により前記炭素繊維の表面に前記Ｓｉ層を形成する場合は、Ｓｉ層の膜厚が理論値で１００ｎｍ以上となるように、成膜時間を調整することが、前記炭素繊維が露出する部分が無い又はほとんど無いように、前記炭素繊維の表面全体に均一な膜厚で前記Ｓｉ層を形成しやすい点から好ましい。また、Ｓｉ層の膜厚が理論値で３００ｎｍ以下となるように成膜時間を調整することが、負極活物質複合体間でのＳｉ層同士の付着を抑制しやすい点から好ましい。
なお、バレルスパッタリング法により形成されるＳｉ層の膜厚の理論値は、下記式（１）により算出することができる。下記式（１）において、装置の被覆係数は、炭素繊維以外のカバー等に付着する分を除くために乗じる係数であり、炭素繊維へのコート量（観察値）とＳｉターゲットの重量減少量から求めることができる装置固有の値である。
When the Si layer is formed on the surface of the carbon fiber by barrel sputtering, the film formation time is adjusted so that the film thickness of the Si layer is theoretically 100 nm or more, so that the carbon fiber is exposed. It is preferable from the viewpoint that the Si layer can be easily formed with a uniform thickness on the entire surface of the carbon fiber so that there are no or almost no portions. In addition, it is preferable to adjust the film formation time so that the film thickness of the Si layer is theoretically 300 nm or less, from the viewpoint of easily suppressing the adhesion of the Si layers between the negative electrode active material composites.
The theoretical value of the film thickness of the Si layer formed by the barrel sputtering method can be calculated by the following formula (1). In the following formula (1), the coating coefficient of the device is a coefficient that is multiplied to remove the amount that adheres to the cover other than the carbon fiber, and from the amount of coating on the carbon fiber (observed value) and the amount of weight reduction of the Si target It is a device-specific value that can be determined.
４．全固体電池用負極活物質複合体の特性
本開示の全固体電池用負極活物質複合体は、前記炭素繊維の表面に、均一性に優れた前記Ｓｉ層を有するため、それ自体も繊維状である。本開示の全固体電池用負極活物質複合体の繊維径は、特に限定はされないが、全固体電池の負極活物質として用いた場合に、電極内の反応が均一になりやすく、副反応が抑制されやすい点から、２０ｎｍ以上４００ｎｍ以下の範囲内であることが好ましく、２５ｎｍ以上３７０ｎｍ以下の範囲内であることがより好ましい。全固体電池用負極活物質複合体の繊維長は、特に限定はされないが、全固体電池の負極活物質として用いた場合に、電極内の反応が均一になりやすく、副反応が抑制されやすい点から、１μｍ以上であることが好ましい。
4. Characteristics of negative electrode active material composite for all-solid-state battery The negative electrode active material composite for an all-solid-state battery of the present disclosure has the Si layer with excellent uniformity on the surface of the carbon fiber, and therefore itself is also fibrous. be. The fiber diameter of the negative electrode active material composite for an all-solid-state battery of the present disclosure is not particularly limited, but when used as a negative electrode active material for an all-solid-state battery, the reaction in the electrode tends to be uniform, and side reactions are suppressed. In view of the fact that the thickness is easily formed, the thickness is preferably in the range of 20 nm or more and 400 nm or less, and more preferably in the range of 25 nm or more and 370 nm or less. The fiber length of the negative electrode active material composite for all-solid-state batteries is not particularly limited, but when used as the negative electrode active material for all-solid-state batteries, the reaction in the electrode tends to be uniform, and side reactions are easily suppressed. Therefore, it is preferably 1 μm or more.
また、本開示の全固体電池用負極活物質複合体は、負極活物質複合体間で表面のＳｉ層同士が付着し難く、全固体電池の保存特性を向上し易い点から、全固体電池の負極に含有させる前において、不織布等のシート状ではなく、分散媒に分散可能な状態であることが好ましい。 In addition, in the negative electrode active material composite for an all-solid-state battery of the present disclosure, it is difficult for the Si layers on the surfaces of the negative electrode active material composites to adhere to each other, and the storage characteristics of the all-solid-state battery are easily improved. Before being contained in the negative electrode, it is preferably in a state dispersible in a dispersion medium rather than in a sheet form such as a nonwoven fabric.
５．全固体電池用負極
本開示の全固体電池用負極は、少なくとも前記本開示の全固体電池用負極活物質複合体を含有することを特徴とする。
5. All-Solid-Battery Negative Electrode The all-solid-state battery negative electrode of the present disclosure is characterized by containing at least the all-solid-state battery negative electrode active material composite of the present disclosure.
本開示の全固体電池用負極は、例えば、少なくとも前記本開示の全固体電池用負極活物質複合体を含有する負極活物質層を有し、必要に応じて、前記負極活物質層の集電を行う負極集電体等のその他の構成を更に有するものとすることができる。
前記負極活物質層は、必要に応じて、固体電解質、導電助剤及びバインダー等を更に含有していてもよく、効果を損なわない範囲において、前記本開示の全固体電池用負極活物質複合体とは異なるその他の負極活物質を更に含有していてもよい。
The negative electrode for an all-solid-state battery of the present disclosure, for example, has a negative electrode active material layer containing at least the negative electrode active material composite for an all-solid-state battery of the present disclosure, and if necessary, the current collection of the negative electrode active material layer. It can further have other configurations such as a negative electrode current collector that performs
The negative electrode active material layer may further contain a solid electrolyte, a conductive aid, a binder, etc. as necessary, and the negative electrode active material composite for an all-solid-state battery of the present disclosure to the extent that the effect is not impaired. It may further contain other negative electrode active material different from.
前記その他の負極活物質としては、例えば、ケイ素、ケイ素合金等の合金系負極活物質；黒鉛（グラファイト）等の炭素材料；Ｌｉ４Ｔｉ５Ｏ１２等の金属酸化物等が挙げられ、中でも、高容量化の観点から、合金系負極活物質が好ましく、ケイ素及びケイ素合金からなる群より選ばれる少なくとも１種がより好ましい。ケイ素合金としては、例えば、Ｓｉ－Ａｌ系合金、Ｓｉ－Ｓｎ系合金、Ｓｉ－Ｇｅ系合金等を挙げることができる。
前記負極活物質層は、前記本開示の全固体電池用負極活物質複合体と、前記合金系負極活物質とを組み合わせて含有することが、全固体電池の保存特性を向上しながら、高容量化できる点から好ましい。
Examples of other negative electrode active materials include alloy - based negative electrode active materials such as silicon and silicon alloys; carbon materials such as graphite; and metal oxides such as Li4Ti5O12 . From the viewpoint of increasing capacity, alloy-based negative electrode active materials are preferred, and at least one selected from the group consisting of silicon and silicon alloys is more preferred. Silicon alloys include, for example, Si—Al based alloys, Si—Sn based alloys, Si—Ge based alloys, and the like.
The negative electrode active material layer contains a combination of the negative electrode active material composite for an all-solid-state battery of the present disclosure and the alloy-based negative electrode active material, thereby improving the storage characteristics of the all-solid-state battery and increasing the capacity. It is preferable because it can be
前記負極活物質層が含有していてもよい固体電解質、導電助剤及びバインダー等の負極活物質以外の成分は、全固体電池に従来用いられている公知ものを用いることができ、特に限定はされない。
固体電解質としては、イオン伝導性が高い点から、硫化物固体電解質が好ましい。
導電助剤としては、例えば、例えば、アセチレンブラック、ケッチェンブラック、カーボンファイバー、ＶＧＣＦ(気相法炭素繊維)等を挙げることができる。
バインダーとしては、例えば、ポリテトラフルオロエチレン（ＰＴＦＥ）、ポリフッ化ビニリデン（ＰＶｄＦ）等のフッ素含有バインダー等を挙げることができる。
Components other than the negative electrode active material, such as the solid electrolyte, the conductive aid, and the binder, which may be contained in the negative electrode active material layer, may be known components conventionally used in all-solid-state batteries, and are not particularly limited. not.
As the solid electrolyte, a sulfide solid electrolyte is preferable because of its high ion conductivity.
Examples of conductive aids include acetylene black, ketjen black, carbon fiber, VGCF (vapor-grown carbon fiber), and the like.
Examples of binders include fluorine-containing binders such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF).
本開示の全固体電池用負極は、前記負極活物質層の集電を行う負極集電体を有していてもよい。前記負極集電体の材料としては、例えばＳＵＳ、銅、ニッケルおよびカーボン等を挙げることができる。 The negative electrode for an all-solid-state battery of the present disclosure may have a negative electrode current collector that collects current from the negative electrode active material layer. Examples of materials for the negative electrode current collector include SUS, copper, nickel and carbon.
本開示の全固体電池用負極の製造方法は、前述した本開示の全固体電池用負極が得られる方法であればよく、公知の方法を用いることができ、特に限定はされない。
本開示の全固体電池用負極が有する前記負極活物質層を形成する方法としては、例えば、前記負極活物質層を構成する各成分を含む負極活物質層用原料の粉末又はペレットを圧縮成形する方法、及び、前記負極活物質層を構成する各成分に更に分散媒を加えて混合して得られる負極合材用原料のスラリー又はペーストを塗布、乾燥する方法等が挙げられる。
The method for producing the all-solid-state battery negative electrode of the present disclosure is not particularly limited as long as it is a method by which the all-solid-state battery negative electrode of the present disclosure can be obtained, and a known method can be used.
As a method for forming the negative electrode active material layer of the negative electrode for an all-solid-state battery of the present disclosure, for example, a powder or pellet of a raw material for a negative electrode active material layer containing each component constituting the negative electrode active material layer is compression-molded. and a method of coating and drying a slurry or paste of a raw material for a negative electrode mixture obtained by further adding a dispersion medium to each component constituting the negative electrode active material layer and mixing them.
本開示の全固体電池用負極が用いられる全固体電池としては、例えば、正極と、前記本開示の全固体電池用負極と、前記正極と前記全固体電池用負極との間に配置された固体電解質層とを備えるものを挙げることができる。前記正極及び前記固体電解質層としては、全固体電池に従来用いられている公知のものを用いることができ、特に限定はされない。
本開示の全固体電池用負極が用いられる全固体電池は、典型的にはリチウムイオン電池であり、一次電池であってもよく、二次電池であってもよいが、中でも、繰り返し充放電でき、例えば車載用電池として有用な点から、二次電池であることが好ましい。なお、一次電池には、二次電池の一次電池的使用（充電後、一度の放電だけを目的とした使用）も含まれる。
Examples of all-solid-state batteries using the all-solid-state battery negative electrode of the present disclosure include, for example, a positive electrode, the all-solid-state battery negative electrode of the present disclosure, and a solid disposed between the positive electrode and the all-solid-state battery negative electrode and an electrolyte layer. As the positive electrode and the solid electrolyte layer, known materials conventionally used in all-solid-state batteries can be used, and are not particularly limited.
The all-solid-state battery using the all-solid-state battery negative electrode of the present disclosure is typically a lithium-ion battery, and may be a primary battery or a secondary battery. , for example, a secondary battery is preferable from the viewpoint of its usefulness as an in-vehicle battery. The primary battery also includes a secondary battery that is used as a primary battery (used for the purpose of discharging only once after being charged).
［実施例１］
（１）全固体電池用負極活物質複合体の作製
ＶＧＣＦ（気相法炭素繊維）（昭和電工製、ＶＧＣＦ（登録商標）－Ｈ）の表面に、バレルスパッタ装置（フルヤ金属製）を用いて、Ｓｉ層を形成することにより、Ｓｉを４５質量％含有する実施例１の全固体電池用負極活物質複合体を得た。Ｓｉの含有量は、負極活物質複合体の総量を１００質量％としたときのＳｉの含有割合である。なお、Ｓｉ層の成膜時間は、前記式（１）により算出されるＳｉ層の膜厚の理論値が１０１ｎｍとなるように調整した。
[Example 1]
(1) Preparation of negative electrode active material composite for all-solid-state battery On the surface of VGCF (vapor-grown carbon fiber) (manufactured by Showa Denko, VGCF (registered trademark)-H), using a barrel sputtering device (manufactured by Furuya Metal) , to obtain a negative electrode active material composite for an all-solid-state battery of Example 1 containing 45% by mass of Si by forming a Si layer. The content of Si is the content ratio of Si when the total amount of the negative electrode active material composite is 100% by mass. The film formation time of the Si layer was adjusted so that the theoretical value of the film thickness of the Si layer calculated by the above formula (1) was 101 nm.
（２）Ｓｉ層の膜厚の変動係数の測定
実施例１の全固体電池用負極活物質複合体をエポキン樹脂で樹脂包埋したサンプルを作製し、当該サンプルをイオンミリングして得た断面を、走査型電子顕微鏡（ＳＥＭ）にて観察した。観察されたＳＥＭ画像を図２に示す。前記サンプルの断面のＳＥＭ画像から、負極活物質複合体が長手方向に垂直な方向で切断された断面として、図２に示す断面Ｓ１～Ｓ７を選択した。当該断面Ｓ１～Ｓ７から、炭素繊維の表面全体がＳｉ層に被覆されていることが確認された。当該断面Ｓ１～Ｓ７の各々において、前述した方法で、Ｓｉ層の膜厚を８方向で測定した。Ｓｉ層の膜厚の測定値の平均値及び標準偏差を算出し、標準偏差を平均値で除してなる変動係数を求めた。断面Ｓ１～Ｓ７の各々において、Ｓｉ層の膜厚の変動係数は０．４以下であった。実施例１で得た全固体電池用負極活物質複合体の断面Ｓ１～Ｓ７におけるＳｉ層の膜厚の測定値、平均値、標準偏差、及び変動係数を表１に示す。
(2) Measurement of the coefficient of variation of the film thickness of the Si layer A sample was prepared by embedding the negative electrode active material composite for an all-solid-state battery of Example 1 in epoxy resin, and the cross section obtained by ion milling the sample was taken. , under a scanning electron microscope (SEM). The observed SEM image is shown in FIG. From the SEM images of the cross sections of the samples, cross sections S1 to S7 shown in FIG. 2 were selected as cross sections obtained by cutting the negative electrode active material composite in a direction perpendicular to the longitudinal direction. From the cross sections S1 to S7, it was confirmed that the entire surface of the carbon fiber was covered with the Si layer. In each of the cross sections S1 to S7, the film thickness of the Si layer was measured in eight directions by the method described above. The average value and standard deviation of the measured values of the film thickness of the Si layer were calculated, and the coefficient of variation obtained by dividing the standard deviation by the average value was obtained. The variation coefficient of the film thickness of the Si layer was 0.4 or less in each of the cross sections S1 to S7. Table 1 shows the measured values, average values, standard deviations, and coefficients of variation of the thickness of the Si layer in cross sections S1 to S7 of the negative electrode active material composite for an all-solid-state battery obtained in Example 1.
（３）評価用全固体電池の作製
（３－１）全固体電池用正極シートの作製
分散媒としての酪酸ブチルに、パインダーとしてのポリフッ化ビニリデンを溶解した５質量％酪酸ブチル溶液、正極活物質としてのニオブ酸リチウムでコーティングされたＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３０２、固体電解質としてのＬｉ２Ｓ－Ｐ２Ｓ５系ガラスセラミック、及び導電助剤としてのＶＧＣＦ（気相法炭素繊維）を、ポリプロピレン製容器に加えて、超音波分散装置（エスエムテー製、製品名ＵＨ－５０）で３０秒間撹拌した。その後、ポリプロピレン製容器を振とう器(柴田科学株式会社製、製品名ＴＴＭ－１)で３分間振とうし、さらに超音波分散装置で３０秒間撹袢して、正極活物質層用ペーストを作製した。前記正極活物質層用ペーストを、アプリケーターを使用して、ドクターブレード法にて、正極集電体としてのアルミニウム箔に塗工し、その後、１００℃に加熱したホットプレート上で３０分間乾燥することにより、正極活物質層を形成し、アルミニウム箔上に正極活物質層が形成された全固体電池用正極シートを作製した。
(3) Production of all-solid-state battery for evaluation (3-1) Production of positive electrode sheet for all-solid-state battery 5 mass% butyl butyrate solution in which polyvinylidene fluoride as a binder is dissolved in butyl butyrate as a dispersion medium, positive electrode active material LiNi 1/3 Co 1/3 Mn 1/3 O 2 coated with lithium niobate as the solid electrolyte, Li 2 SP 2 S 5 -based glass-ceramic as the solid electrolyte, and VGCF (gas phase Lawn carbon fiber) was added to a polypropylene container and stirred for 30 seconds with an ultrasonic dispersion device (manufactured by SMT, product name UH-50). Thereafter, the polypropylene container was shaken with a shaker (manufactured by Shibata Scientific Co., Ltd., product name TTM-1) for 3 minutes, and further stirred with an ultrasonic dispersion device for 30 seconds to prepare a positive electrode active material layer paste. did. The positive electrode active material layer paste is applied to an aluminum foil as a positive electrode current collector by a doctor blade method using an applicator, and then dried on a hot plate heated to 100 ° C. for 30 minutes. A positive electrode sheet for an all-solid battery, in which a positive electrode active material layer was formed on an aluminum foil, was produced.
（３－２）全固体電池用負極シートの作製
分散媒としての酪酸ブチル、バインダーとしてのポリフッ化ビニリデンを溶解した５質量％酪酸ブチル溶液、負極活物質としての前記実施例１の全固体電池用負極活物質複合体、固体電解質としてのＬｉ２Ｓ－Ｐ２Ｓ５系ガラスセラミック、及び導電助剤としてのＶＧＣＦ（気相法炭素繊維）を、ポリプロピレン製容器に加えて、超音波分散装置で３０秒間撹拌した。その後、ポリプロピレン製容器を振とう器で３０分間振とうして、負極活物質層用ペーストを作製した。前記負極活物質層用ペーストを、アプリケーターを使用して、ドクターブレード法にて、負極集電体としての銅箔に塗工し、その後、１００℃に加熱したホットプレート上で３０分間乾燥することにより、負極活物質層を形成し、銅箔上に負極活物質層が形成された全固体電池用負極シートを作製した。
(3-2) Production of negative electrode sheet for all-solid-state battery Butyl butyrate as dispersion medium, 5% by mass butyl butyrate solution in which polyvinylidene fluoride is dissolved as binder, all-solid-state battery of Example 1 as negative electrode active material A negative electrode active material composite, a Li 2 SP 2 S 5 glass ceramic as a solid electrolyte, and VGCF (vapor-grown carbon fiber) as a conductive aid were added to a polypropylene container, and subjected to an ultrasonic dispersing device. Stir for 30 seconds. After that, the polypropylene container was shaken with a shaker for 30 minutes to prepare a negative electrode active material layer paste. The negative electrode active material layer paste is applied to a copper foil as a negative electrode current collector by a doctor blade method using an applicator, and then dried on a hot plate heated to 100 ° C. for 30 minutes. Thus, a negative electrode sheet for an all-solid-state battery in which a negative electrode active material layer was formed on a copper foil was produced.
（３－３）固体電解質シートの作製
分散媒としてのヘプタンに、バインダーとしてのブタジエンゴムを溶解した５質量％ヘプタン溶液、及び固体電解質としてのヨウ化リチウムを含有するＬｉ２Ｓ－Ｐ２Ｓ５系ガラスセラミックを、ポリプロピレン製容器に加えて、超音波分散装置で３０秒間撹拌した。その後、ポリプロピレン製容器を振とう器で３０分間振とうして、固体電解質層用ペーストを作製した。前記固体電解質層用ペーストを、アプリケーターを使用して、ブレード法にて、基盤としてのアルミニウム箔に塗工し、その後、１００℃に加熱したホットプレート上で３０分間乾燥することにより、固体電解質層を形成し、アルミニウム箔上に固体電解質層が形成された固体電解質シートを作製した。
(3-3) Production of Solid Electrolyte Sheet Li 2 SP 2 S 5 containing a 5% by mass heptane solution in which butadiene rubber as a binder is dissolved in heptane as a dispersion medium, and lithium iodide as a solid electrolyte. The system glass-ceramic was added to a polypropylene container and stirred for 30 seconds with an ultrasonic disperser. After that, the polypropylene container was shaken with a shaker for 30 minutes to prepare a solid electrolyte layer paste. The solid electrolyte layer paste is applied to an aluminum foil as a substrate by a blade method using an applicator, and then dried on a hot plate heated to 100° C. for 30 minutes to form a solid electrolyte layer. was formed to prepare a solid electrolyte sheet in which a solid electrolyte layer was formed on an aluminum foil.
（３－４）積層、プレス工程
固体電解質層が正極活物質層と接するように、前記固体電解質シートを前記全固体電池用正極シート上に積層して、１ｔｏｎ／ｃｍ２でプレスし、固体電解質層の基盤としてのアルミニウム箔を剥がすことにより、固体電解質層と、正極活物質層と、正極集電体としてのアルミ箔とがこの順に積層された積層体を作製した。その後、この積層体の固体電解質層側に、固体電解質層が負極活物質層と接するように、前記全固体電池用負極シートを重ねてプレスすることにより、負極集電体としての銅箔と、負極活物質層と、固体電解質層と、正極活物質層と、正極集電体としてのアルミ箔とがこの順に積層された全固体電池（セル）を作製した。作製したセルは拘束治具を用いて２Ｎ・ｍの拘束圧にて拘束し、デシケーターに入れて下記評価を行った。
(3-4) Lamination and pressing step The solid electrolyte sheet is laminated on the positive electrode sheet for an all-solid battery so that the solid electrolyte layer is in contact with the positive electrode active material layer, and pressed at 1 ton/cm 2 to form a solid electrolyte. By peeling off the aluminum foil as the layer base, a laminate was produced in which the solid electrolyte layer, the positive electrode active material layer, and the aluminum foil as the positive electrode current collector were laminated in this order. After that, the all-solid-state battery negative electrode sheet is overlaid and pressed on the solid electrolyte layer side of the laminate so that the solid electrolyte layer is in contact with the negative electrode active material layer, thereby obtaining a copper foil as a negative electrode current collector, An all-solid battery (cell) was fabricated in which a negative electrode active material layer, a solid electrolyte layer, a positive electrode active material layer, and an aluminum foil as a positive electrode current collector were laminated in this order. The produced cell was constrained with a constraining pressure of 2 N·m using a constraining jig, placed in a desiccator, and subjected to the following evaluations.
（４）評価
（４－１）保存特性評価
前記評価用全固体電池を初期充電として１０時間率（１／１０［Ｃ］）で４．５５Ｖまで定電流－定電圧充電（終止電流１／１００［Ｃ］）してから、初期放電として定電流－定電圧放電で２．５０Ｖまで放電した。その後、３時間率（１／３［Ｃ］）で４．３５Ｖまで定電流－定電圧充電（終止電流１／１００［Ｃ］）した後、６０℃で２週間保存した。前記充電直後を保存前とする。保存前後でそれぞれ、３時間率（１／３［Ｃ］）で４．３５Ｖまで定電流－定電圧充電（終止電流１／１００［Ｃ］）してから、定電流－定電圧放電で３．００Ｖまで放電して、放電容量を測定した。保存後容量維持率（％）＝（保存後放電容量／保存前放電容量）×１００の式により、保存後容量維持率を算出した。結果を表２に示す。保存後容量維持率が１００％に近いほど、保存特性に優れる。
(4) Evaluation (4-1) Storage characteristic evaluation The all-solid-state battery for evaluation is initially charged at a 10-hour rate (1/10 [C]) to 4.55 V at a constant current-constant voltage charge (final current 1/100 [C]), and then discharged to 2.50 V by constant current-constant voltage discharge as initial discharge. Then, after constant current-constant voltage charging (final current 1/100 [C]) to 4.35 V at a rate of 3 hours (1/3 [C]), the battery was stored at 60° C. for 2 weeks. Immediately after the charging is defined as before storage. Before and after storage, constant current-constant voltage charge (final current 1/100 [C]) to 4.35 V at a rate of 3 hours (1/3 [C]), then constant current-constant voltage discharge. After discharging to 00 V, the discharge capacity was measured. The post-storage capacity retention rate (%) was calculated according to the formula: (discharge capacity after storage/discharge capacity before storage)×100. Table 2 shows the results. The closer the post-storage capacity retention rate is to 100%, the better the storage characteristics.
（４－２）サイクル特性評価
前記評価用全固体電池を、初期充電として１０時間率（１／１０［Ｃ］）で４．５５Ｖまで定電流－定電圧充電（終止電流１／１００［Ｃ］）してから、初期放電として定電流－定電圧放電で２．５０Ｖまで放電した。その後、３時間率（１／３［Ｃ］）で４．３５Ｖまで定電流－定電圧充電（終止電流１／１００［Ｃ］）してから、定電流－定電圧放電で３．００Ｖまで放電し、電池をＳＯＣ２０％に調整して、定電流（７［Ｃ］）で５秒間放電し、電流と電圧の低下から、サイクル試験前のＳＯＣ２０％の抵抗を求めた。その後、サイクル試験として、０．５時間率（２［Ｃ］）で、４．１７Ｖまで充電した後に、３．１７Ｖまで放電を行うサイクルを３００回繰り返して行った。前記サイクル試験後に、３時間率（１／３［Ｃ］）で４．３５Ｖまで定電流－定電圧充電（終止電流１／１００［Ｃ］）してから、定電流－定電圧放電で３．００Ｖまで放電し、電池をＳＯＣ２０％に調整して、定電流（７［Ｃ］）で５秒間放電し、電流と電圧の低下から、サイクル試験後のＳＯＣ２０％の抵抗を求めた。サイクル試験前後のＳＯＣ２０％の抵抗を表２に示す。
(4-2) Cycle characteristic evaluation The all-solid-state battery for evaluation is charged at a constant current-constant voltage charge to 4.55 V at a rate of 10 hours (1/10 [C]) as an initial charge (final current 1/100 [C] ), and then discharged to 2.50 V by constant current-constant voltage discharge as initial discharge. After that, constant current-constant voltage charge (final current 1/100 [C]) to 4.35 V at 3 hour rate (1/3 [C]), then discharge to 3.00 V with constant current-constant voltage discharge. Then, the battery was adjusted to SOC 20%, discharged at a constant current (7 [C]) for 5 seconds, and the resistance at SOC 20% before the cycle test was obtained from the drop in current and voltage. Thereafter, as a cycle test, a cycle of charging to 4.17 V and then discharging to 3.17 V at a rate of 0.5 hours (2[C]) was repeated 300 times. After the cycle test, constant current-constant voltage charging (final current 1/100 [C]) to 4.35 V at a rate of 3 hours (1/3 [C]), followed by constant current-constant voltage discharging to 3. The battery was discharged to 00 V, adjusted to SOC 20%, discharged at a constant current (7 [C]) for 5 seconds, and the resistance at SOC 20% after the cycle test was determined from the drop in current and voltage. Table 2 shows the resistance at SOC 20% before and after the cycle test.
［参考例１、２］
実施例１の前記（１）全固体電池用負極活物質複合体の作製において、Ｓｉ層の成膜時間を、Ｓｉ層の膜厚の理論値が表２に示す値となるように調整した以外は、実施例１と同様にして、参考例１、２の全固体電池用負極活物質複合体を得た。参考例１、２の全固体電池用負極活物質複合体におけるＳｉの含有量を表２に示す。
実施例１で得た全固体電池用負極活物質複合体に代えて、参考例１、２の全固体電池用負極活物質複合体を用いた以外は、実施例１と同様にして、参考例１、２の評価用全固体電池を作製し、実施例１と同様の評価を行った。
[Reference Examples 1 and 2]
In Example 1 (1) Preparation of negative electrode active material composite for all-solid-state battery, the film formation time of the Si layer was adjusted so that the theoretical value of the film thickness of the Si layer was the value shown in Table 2. obtained negative electrode active material composites for all-solid-state batteries of Reference Examples 1 and 2 in the same manner as in Example 1. Table 2 shows the Si content in the negative electrode active material composites for all-solid-state batteries of Reference Examples 1 and 2.
Reference Example was carried out in the same manner as in Example 1, except that the all-solid-state battery negative electrode active material composites of Reference Examples 1 and 2 were used instead of the all-solid-state battery negative electrode active material composites obtained in Example 1. Evaluation all-solid-
［比較例１］
実施例１の前記（３）評価用全固体電池の作製において、実施例１で得た全固体電池用負極活物質複合体に代えて、Ｓｉ（高純度化学研究所製、Ｓｉ粉末、平均粒径約５μｍ）を用いた以外は、実施例１と同様にして、比較例１の評価用全固体電池を作製し、実施例１と同様の評価を行った。
[Comparative Example 1]
In the preparation of the (3) all-solid-state battery for evaluation in Example 1, instead of the negative electrode active material composite for the all-solid-state battery obtained in Example 1, Si (manufactured by Kojundo Chemical Laboratory Co., Ltd., Si powder, average grain An evaluation all-solid-state battery of Comparative Example 1 was produced in the same manner as in Example 1 except that a diameter of about 5 μm was used, and the same evaluation as in Example 1 was performed.
［比較例２］
実施例１で得た全固体電池用負極活物質複合体を用いて、下記手順により評価用電解液電池を作製した。
バインダーとしてのポリフッ化ビニリデン（ＰＶｄＦ）を溶解させた固形分５質量％のＮ－メチルピロリドン（ＮＭＰ）溶液６．０ｇに、導電助剤としてのアセチレンブラック（ＡＢ）を０．８ｇ加え、５分間混合した。次いで、正極活物質としてのＬｉＮｉ１／３Ｃｏ１／３Ｍｎ１／３Ｏ２を８．９ｇ加え、１０分間混合した。そして、適度な塗工性となるようにＮＭＰを加えて粘度を調整し、質量比が正極活物質：ＰＶｄＦ：ＡＢ＝８９：８：３のスラリー状組成物を調製した。得られた組成物を、正極集電体としての厚さ１５μｍのアルミニウム箔に、ドクターブレードを用いて手動で塗工し、乾燥およびロールプレスして、正極活物質層を形成し、アルミニウム箔上に正極活物質層が形成された電解液電池用正極シートを作製した。
一方で、バインダーとしてのポリイミドワニスを溶解させた固形分１８質量％のＮＭＰ溶液２．８ｇに、ＮＭＰを更に２．４ｇ加え、５分間混合した。次いで、導電助剤としてのＶＧＣＦ（気相法炭素繊維）を０．５ｇ加え、５分間混合した。次いで、負極活物質としての前記実施例１で得た全固体電池用負極活物質複合体を１０ｇ加え、１０分間混合した。そして、適度な塗工性となるようにＮＭＰを加えて粘度を調整し、質量比が負極活物質：ポリイミドワニス：ＶＧＣＦ＝９１：４．５：４．５のスラリー状組成物を調製した。得られた組成物を、負極集電体としての厚さ１０μｍの銅箔に、ドクターブレードを用いて手動で塗工し、乾燥およびロールプレスした後、不活性ガス下、３５０℃で２時間熱処理してバインダーをポリイミド化させて、負極活物質層を形成し、銅箔上に負極活物質層が形成された電解液電池用負極シートを作製した。
一方で、エチレンカーボネート（ＥＣ）と、ジエチルカーボネート（ＤＥＣ）とを、３：７の体積比で含む混合溶媒に、ＬｉＰＦ６を１ｍｏｌ／Ｌの濃度となるように溶解させて、非水電解液を調製した。
次に、前記電解液電池用正極シート及び前記電解液電池用負極シートを所定の大きさに切り出して、セパレータを介して、正極活物質層と負極活物質層とを対向させた状態でコイン型セルに収容し、前記非水電解液を注液することで、評価用電解液電池を作製した。なお、セパレータとしては、ポリエチレン（ＰＥ）層の両面にポリプロピレン（ＰＰ）層が積層された三層構造のものを使用した。
[Comparative Example 2]
Using the negative electrode active material composite for an all-solid-state battery obtained in Example 1, an electrolytic solution battery for evaluation was produced by the following procedure.
Add 0.8 g of acetylene black (AB) as a conductive aid to 6.0 g of N-methylpyrrolidone (NMP) solution with a solid content of 5% by mass in which polyvinylidene fluoride (PVdF) as a binder is dissolved, and add 0.8 g for 5 minutes. Mixed. Then, 8.9 g of LiNi 1/3 Co 1/3 Mn 1/3 O 2 as a positive electrode active material was added and mixed for 10 minutes. Then, NMP was added to adjust the viscosity so as to provide appropriate coatability, and a slurry composition having a mass ratio of positive electrode active material:PVdF:AB=89:8:3 was prepared. The obtained composition was manually applied to an aluminum foil having a thickness of 15 μm as a positive electrode current collector using a doctor blade, dried and roll-pressed to form a positive electrode active material layer, and then coated on the aluminum foil. A positive electrode sheet for an electrolytic solution battery was prepared, in which a positive electrode active material layer was formed on the substrate.
On the other hand, 2.4 g of NMP was further added to 2.8 g of NMP solution having a solid content of 18% by mass in which polyimide varnish as a binder was dissolved, and mixed for 5 minutes. Then, 0.5 g of VGCF (vapor grown carbon fiber) as a conductive aid was added and mixed for 5 minutes. Next, 10 g of the negative electrode active material composite for an all-solid-state battery obtained in Example 1 was added as a negative electrode active material, and mixed for 10 minutes. Then, NMP was added to adjust the viscosity so as to provide appropriate coatability, and a slurry composition having a mass ratio of negative electrode active material:polyimide varnish:VGCF=91:4.5:4.5 was prepared. The obtained composition was manually applied to a copper foil having a thickness of 10 μm as a negative electrode current collector using a doctor blade, dried and roll-pressed, and then heat-treated at 350° C. for 2 hours under an inert gas. Then, the binder was polyimideized to form a negative electrode active material layer, and a negative electrode sheet for an electrolytic solution battery in which the negative electrode active material layer was formed on the copper foil was produced.
On the other hand, LiPF 6 was dissolved in a mixed solvent containing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7 to a concentration of 1 mol/L to form a non-aqueous electrolyte. was prepared.
Next, the positive electrode sheet for electrolyte batteries and the negative electrode sheet for electrolyte batteries are cut into a predetermined size, and the positive electrode active material layer and the negative electrode active material layer are opposed to each other with a separator interposed therebetween. An evaluation electrolyte battery was produced by housing the battery in a cell and injecting the non-aqueous electrolyte. The separator used had a three-layer structure in which polypropylene (PP) layers were laminated on both sides of a polyethylene (PE) layer.
比較例２の評価用電解液電池について、実施例１で行った評価の初期充電を４．３５Ｖまでの充電に変更した以外は、実施例１と同様にして評価を行った。 The electrolyte battery for evaluation of Comparative Example 2 was evaluated in the same manner as in Example 1, except that the initial charging in the evaluation performed in Example 1 was changed to charging up to 4.35V.
［比較例３］
比較例２において、実施例１で得た全固体電池用負極活物質複合体に代えて、比較例１と同様のＳｉを用いた以外は、比較例２と同様にして、比較例３の評価用電解液電池を作製した。
比較例３の評価用電解液電池について、実施例１で行った評価の初期充電を４．３５Ｖまでの充電に変更した以外は、実施例１と同様にして評価を行った。
[Comparative Example 3]
Comparative Example 3 was evaluated in the same manner as in Comparative Example 2 except that the same Si as in Comparative Example 1 was used instead of the negative electrode active material composite for an all-solid-state battery obtained in Example 1. We fabricated an electrolyte battery for
The electrolyte battery for evaluation of Comparative Example 3 was evaluated in the same manner as in Example 1, except that the initial charging in the evaluation in Example 1 was changed to charging up to 4.35V.
表２に示すように、実施例１で得た本開示の全固体電池用負極活物質複合体を負極活物質として用いた全固体電池では、Ｓｉを負極活物質として用いた比較例１の全固体電池に比べ、保存後の容量維持率が高く、保存特性が向上しており、また、サイクル試験前後において抵抗が低かった。
参考例１、２で得た全固体電池用負極活物質複合体を負極活物質として用いた全固体電池も、比較例１の全固体電池に比べ、保存後の容量維持率が高く、保存特性が向上しており、また、サイクル試験前後において抵抗が低かった。参考例１、２で得た全固体電池用負極活物質複合体は、炭素繊維の長手方向に垂直な方向に切断した断面内でのＳｉ層の膜厚の変動係数が０．４以下であると考えられる。
As shown in Table 2, in the all-solid-state battery using the negative electrode active material composite for an all-solid-state battery of the present disclosure obtained in Example 1 as the negative electrode active material, all of Comparative Example 1 using Si as the negative electrode active material Compared to the solid battery, the capacity retention rate after storage was high, the storage characteristics were improved, and the resistance was low before and after the cycle test.
The all-solid-state battery using the all-solid-state battery negative electrode active material composite obtained in Reference Examples 1 and 2 as the negative electrode active material also has a higher capacity retention rate after storage than the all-solid-state battery of Comparative Example 1, and has excellent storage characteristics. was improved, and the resistance was low before and after the cycle test. In the negative electrode active material composites for all-solid-state batteries obtained in Reference Examples 1 and 2, the coefficient of variation of the thickness of the Si layer in the cross section cut in the direction perpendicular to the longitudinal direction of the carbon fiber is 0.4 or less. it is conceivable that.
比較例２、３では、固体電解質層に代えて電解液を用いた電解液電池について評価を行った。比較例２では、実施例１で得た本開示の全固体電池用負極活物質複合体を負極活物質として用いたにも関わらず、Ｓｉを負極活物質として用いた比較例３に比べて、保存後の容量維持率が低く、保存特性が低下していた。比較例３で用いたＳｉよりも、比較例２で用いた本開示の全固体電池用負極活物質複合体の方が、電解液と接するＳｉの表面積が大きく、電解液の分解反応が起こりやすかったためと推定される。また、比較例２、３の電解液電池は、サイクル試験後に抵抗が大きく増大しており、全固体電池に比べ、サイクル試験による劣化が大きいことが明らかになった。電解液電池では、電解液とＳｉが接しているため、充放電時に電解液の分解反応が起きて、抵抗の高い被膜が形成されたと考えられる。 In Comparative Examples 2 and 3, an electrolyte solution battery using an electrolyte solution instead of the solid electrolyte layer was evaluated. In Comparative Example 2, although the negative electrode active material composite for an all-solid-state battery of the present disclosure obtained in Example 1 was used as the negative electrode active material, compared to Comparative Example 3 in which Si was used as the negative electrode active material, The capacity retention rate after storage was low, and the storage characteristics were degraded. Compared to Si used in Comparative Example 3, the negative electrode active material composite for an all-solid-state battery of the present disclosure used in Comparative Example 2 has a larger surface area of Si in contact with the electrolyte, and the decomposition reaction of the electrolyte occurs more easily. presumed to be because In addition, the electrolyte batteries of Comparative Examples 2 and 3 showed a large increase in resistance after the cycle test, and it was found that the deterioration due to the cycle test was greater than that of the all-solid-state battery. In the electrolyte battery, since the electrolyte and Si are in contact with each other, the decomposition reaction of the electrolyte occurred during charging and discharging, and a film with high resistance was formed.
１ 炭素繊維
２ Ｓｉ層
１０ 全固体電池用負極活物質複合体
1
Claims (1)
前記炭素繊維の長手方向に垂直な方向に切断した断面内での前記Ｓｉ層の膜厚の変動係数が０．４以下であることを特徴とする、硫化物全固体電池用負極活物質複合体。 Having a carbon fiber and a Si layer covering the surface of the carbon fiber,
A negative electrode active material composite for a sulfide all-solid-state battery, characterized in that the coefficient of variation of the thickness of the Si layer in a cross section cut in a direction perpendicular to the longitudinal direction of the carbon fiber is 0.4 or less. .
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